The present invention relates to medical probes having field transducers used for detecting the disposition of the probe, and to the medical procedures utilizing such probes.
Conventional surgical procedures involve cutting through bodily structures to expose a lesion or organ within the body for treatment. Because these procedures create considerable trauma to the patient, physicians have developed minimally invasive procedures using probes inserted into the body. For example, devices commonly referred to as endoscopes include an elongated body having a distal end and a proximal end. The distal end of the probe body can be inserted into the gastrointestinal tract through a body orifice. The endoscope may be equipped with optical devices such as cameras or fiber optics to permit observation of the tissues surrounding the distal end, and surgery may be performed by inserting and maneuvering surgical instruments through a channel in the endoscope body. Other probes commonly referred to as laparoscopes and arthroscopes are inserted into the body through small holes formed in surrounding tissues to reach the bodily structures to be treated or measured. Still other probes, commonly referred to as catheters, can be advanced through the vascular system, as through a vein or artery, or through other bodily passages such as the urinary tract.
The physician can guide the probe to the desired location within the body by feel or by continuously imaging the probe and the body, as by fluoroscopy, during the procedure. Where the probe includes optical elements, the physician can guide the probe based on visual observation of the tissues surrounding the distal tip of the probe. However, this option is available only for probes such as conventional endoscopes which are large enough to accommodate the optical elements.
As described, for example, in U.S. Pat. Nos. 5,558,091, 5,391,199; 5,443,489; and in PCT International Publication WO 96/05768 Application PCT/US 95/01103, the disclosures of which are hereby incorporated by reference herein, the disposition of a probexe2x80x94its position, orientation, or bothxe2x80x94can be determined by using one or more field transducers such as a Hall effect or magnetoresistive device, coil or other antenna carried on the probe, typically at or adjacent the distal end of the probe, or at a precisely known location relative to the distal end of the probe. One or more additional field transducers disposed outside the body in an external frame of reference. The field transducers preferably are arranged to detect or transmit non-ionizing fields or field components such as a magnetic field, electromagnetic radiation or acoustical energy such as ultrasonic vibration. By transmitting the field between the external reference field transducers and the field transducers on the probe, characteristics of field transmission between these devices can be determined. The position and/or orientation of the field transducer, in the external frame of reference can be deduced from these transmission characteristics. As the field transducer is mounted to the probe, the position of the probe can be determined by determining the position of the field transducer in the external frame of reference. Because the field transducer allows determination of the position of the probe, such a transducer is also referred to as a xe2x80x9cposition sensorxe2x80x9d.
As described, for example, in the aforementioned U.S. Pat. No. 5,558,091, the frame of reference of the external field transducers can be registered with the frame of reference of imaging data such as magnetic resonance imaging data, computerized axial tomographic data, or conventional x-ray image data and hence the position and orientation data derived from the system can be displayed can as a representation of the probe superimposed on an image of the patient""s body. The physician can use this information to guide the probe to the desired location within the patient""s body, and to monitor its orientation during treatment or measurement of the body structure. This arrangement greatly enhances the ability of the physician to navigate the distal end of the probe through bodily structures. It offers significant advantages over conventional methods of navigating probes by feel alone. Because it does not require acquisition of an optical image of the surrounding tissues for navigation purposes, it can be used with probes which are too small to accommodate optical elements. The transducer-based system avoids the difficulties associated with navigation of a probe by continuous imaging of the probe and patient during the procedure. For example, it avoids exposure to ionizing radiation inherent in fluoroscopic systems.
However, still further improvements in transducer-based probe navigation and treatment systems would be desirable. In particular, it would be desirable to provide greater versatility in probe configurations. Thus, the diverse medical procedures require numerous different tools for use within the body. It would be desirable if any such tool could be guided and located in the same manner as the probes discussed above, without the need to adapt or redesign the tool to a accommodate the field transducer or position sensor. It would also be desirable to provide probes in diverse configurations matching different anatomical structures. Merely by way of example, it is sometimes desirable to advance a relatively stiff probe through anatomical structures defining a path having a particular radius of curvature unique to the patient. It is impractical to stock transducer-equipped probes in all of the various configurations required to accommodate different patients. Also, because field transducers can be impaired by exposure to certain sterilization processes, it would be desirable to provide single-use or limited-use field transducers which can be applied to an instrument.
The present invention addresses these and other needs.
One aspect of the present invention provides methods of configuring and operating a probe. A method according to this aspect of the invention preferably includes the steps providing a probe including a first field transducer and a probe body so that the field transducer is disposed in an arbitrary, user-selected disposition relative to a feature of the probe body, such as at an arbitrary disposition relative to the distal end of the probe body. The probe is calibrated by placing the aforesaid feature of the probe body at one or more known dispositions in the frame of reference defined by the external or reference field transducers of the system. While this feature of the probe body is in such known disposition, one or more calibration dispositions of the field transducer in the reference-transducer frame of reference is or are determined by transmitting one or more nonionizing fields between the first field transducer mounted on the probe body the reference field transducers and monitoring one or more characteristics of the fields at one or more of said transducers. The calibration process further includes the step of determining a transform between disposition of the first field transducer and disposition of said feature of said probe body from said one or more calibration dispositions and said one or more known dispositions. After the calibration steps, disposition of said feature of the probe is determined by (1) determining the disposition of the first field transducer by transmitting one or more non-ionizing fields between the first field transducer and said reference field transducers and monitoring one or more characteristics of the fields and (2) applying said transform to the so-determined disposition of the first field transducer.
Because the transform between disposition of the first field transducer and disposition of the probe body feature is determined during the calibration cycle, there is no need for any particular, predetermined spatial relationship between the first field transducer or position sensor and the distal end or other feature of the probe body to be tracked by the system during use. All that is required is that the spatial relationship remain fixed after calibration. Thus, according to this aspect of the invention, there is no need for any special configuration of the probe body; provided that the first field transducer or position sensor can be securely attached to a medical instrument of any type which can be inserted into the patient or contacted with the patient, that medical instrument can serve as an instrumented probe. This aspect of the invention allows the physician to use existing tools and to track the disposition of existing tools in the same manner as a specialized sensor-equipped probe.
The step of providing the probe can include the step of adjusting the probe body to a user-selected configuration, as by bending or otherwise deforming the probe body. In one preferred arrangement, the probe body includes a formable section which can be bent manually by the physician into a desired configuration after review of an image showing the relevant anatomical features, but which thereafter retains its shape. The probe is calibrated after bending. Thus, even if the sensor or first field transducer is mounted remote from the distal tip, the position of the distal tip can be tracked with sufficient accuracy to allow navigation of the tip through the anatomy. In effect, the physician can custom-form a probe as needed for any procedure. A further aspect of the present invention provides a pointing device or probes with a formable distal regions and with a field transducer or position sensor at the distal end, so that the position of the distal end can be monitored even without calibration as discussed above.
The known disposition used in the calibration cycle can be determined using the first field transducer, without the other elements of the probe, as by engaging the first field transducer with a fixed object in the external reference frame and determining disposition of the first field transducer.
A related aspect of the present invention provides components for use in a medical probe system. One component according to this aspect of the invention includes a field transducer as referred to above and a selectively operable mounting element adapted to secure the field transducer to a body of a medical instrument so that the disposition of the field transducer relative to the body of the instrument can be selected from among a range of dispositions. Preferably, such range includes all positions on the body; i.e., the mounting element can secure the field transducer anywhere on the instrument body. A component according to a further, related aspect of the invention includes the field transducer with a selectively operable mounting element adapted to secure the field transducer to any one of a plurality of different medical instruments having bodies of different configurations. In components according to these aspects of the invention, the mounting element may include an adhesive for bonding the field transducer to the instrument body, or else may include a clip attached to the field transducer, the clip being adapted to grip an instrument body.
The calibration steps can be repeated several times for a single feature of the probe body, using the same or different known dispositions and calibration dispositions, so as to enhance the accuracy of the calibration process. Alternatively or additionally, the calibration steps can be performed using more than one feature of a probe, so that a separate transform is developed for each feature. During use, the system can track all of the features for which such calibration steps were performed. For example, where a probe is bent to a user-defined shape, the calibration step can be performed for many points along the probe, and the system can display locations of these many points during use. Thus, the system can display a realistic depiction of the user-defined shape. A disposable device according to a further aspect of the invention includes a field transducer as discussed above, and a mounting element for securing the field transducer to a medical instrument, the mounting element being adapted to engage a body of the medical instrument so that said disposable device cannot be removed readily from the instrument without altering at least one feature of the disposable device. For example, the mounting element may be adapted to engage the instrument so that said device cannot be removed readily from the instrument without deforming or breaking a part of the mounting element. Devices according to related aspects of the invention incorporate the field transducer, a mounting element and a usage monitoring circuit element for recording use of the device. Thus, the usage monitoring circuit element may provide an indication representing the number of times the disposable device has been used or the total time the disposable device has been operatively used. These arrangements help to prevent improper reuse of the device.
The present invention will be better understood from the following detailed description of preferred embodiments of the invention, taken in conjunction with the accompanying drawings.